Known in the art is a so-called “knock type writing instrument” which has an operating part at a back end part of a barrel and in which a knock operation pushing the operating part against a biasing force of a spring arranged inside the barrel is used to cause the instrument to switch to a writing state where a writing part constituted by a tip of a refill holding ink, that is, a writing member, projects out from a front end of the barrel and in which a repeat knock operation or depression of a release part separate from the operating part is used to cause the instrument to switch to a nonwriting state where the writing part is retracted inside the barrel.